Irrigation system with corner irrigator span

ABSTRACT

An irrigation system ( 10 ) for conveying a fluid to a region (A) is provided. The irrigation system ( 10 ) comprises a main irrigation portion ( 16 ) having an end irrigator span ( 44 ). A corner irrigator span ( 42 ) extends radially from the end irrigator span ( 44 ). A control system ( 90 ) controls movement of the corner irrigator span ( 42 ). The control system ( 90 ) includes a linear movement control system ( 92 ) to control a corner drive unit ( 72 ) of the corner irrigator span ( 42 ) and a steering control system ( 94 ) controls a steering unit ( 74 ) of the corner irrigator span ( 42 ). The steering control system ( 94 ) includes a controller ( 100 ) that receives control signals from four electrical generators ( 102,104,106,108 ) to control the steering unit ( 74 ) such that the corner irrigator span ( 42 ) follows along an outer boundary (B) of the region (A). At least one of the electrical generators ( 102,104,106,108 ) is an electronic compass ( 104 ) for sensing a reference signal to determine a primary control position (P) of the main irrigation portion ( 16 ).

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. provisional patentapplication serial No. 60/423,563, filed Nov. 4, 2002.

FIELD OF THE INVENTION

[0002] The present invention relates to an irrigation system forconveying a fluid to a region having a main boundary and an outerboundary outlying the main boundary. More specifically, the presentinvention relates to the irrigation system comprising a main irrigationportion for irrigating the region within the main boundary and a cornerirrigator span extending from the main irrigation portion for irrigatingthe region between the main boundary and the outer boundary.

BACKGROUND OF THE INVENTION

[0003] Conventional irrigation systems include a series ofinterconnected irrigator spans having conduits for conveying fluid to aregion such as an agricultural field. One such irrigation system usedfor this purpose is called a center pivot irrigation system. A typicalcenter pivot irrigation system includes a center pivot tower about whichthe irrigator spans will rotate. The irrigator spans are connected in anend-to-end manner and extend radially from the center pivot tower. Thefluid is pumped from a fluid source through the conduits of eachirrigator span and is applied to the region through discharge nozzlesmounted to the conduits. The irrigation system may include severalirrigator spans capable of reaching tens to hundreds of acres, or theirrigation system may include only a few irrigator spans capable ofreaching only a few acres. Separate drive systems rotate each of theirrigator spans about the center pivot tower.

[0004] The series of irrigator spans extending radially from the centerpivot tower comprise a main irrigation portion of the irrigation system.The main irrigation portion is designed to maintain a relativelyconstant alignment as the main irrigation portion rotates about thecenter pivot tower. The main irrigation portion irrigates the regionwithin a main boundary thereof.

[0005] A corner irrigator span extends radially from the main irrigationportion to access an outer boundary of the region thereby irrigating theregion between the main boundary and the outer boundary. The cornerirrigator span is capable of moving between a position in which thecorner irrigator span is oriented at less than ninety degrees relativeto the main irrigation portion and a position in which the cornerirrigator span is in alignment with the main irrigation portion. Theability of the corner irrigator span to traverse such a wide range ofpositions relative to the main irrigation portion allows the cornerirrigator span to flex out to reach the outer boundary of the region asthe irrigation system is operating. This is particularly useful inrectangular regions in which the corner irrigator span is used to reachfarther into corners of the region.

[0006] A corner drive system is used to move the corner irrigator span.The corner drive system comprises a steering unit having a steeringmotor for steering a set of drive wheels, and a corner drive unit havingdrive motors for driving the drive wheels. Typically, in the prior art,the corner drive system is responsive to a buried conductor thatoutlines the outer boundary of the region. A sensor is mounted on adistal end of the corner irrigator span in which the corner drive systemis located. The sensor is capable of sensing the buried conductor andcontrolling the steering unit accordingly to ensure that the drivewheels follow the buried conductor along the outer boundary of theregion. The primary downfall to such a system is the required depth ofthe buried conductor. Typically, the buried conductor can only becovered by less than one to two feet of earth to ensure properoperation. With such a small amount of cover, machinery such as plows,cultivators, and the like, are likely to disrupt the buried conductor,and at times, rip the buried conductor from the cover completely. Inaddition, the expense to place the buried conductor along the outerboundary can be high.

[0007] To improve on these irrigation systems, the prior art hasattempted to engineer an irrigation system that is devoid of the buriedconductor. Such an irrigation system is shown in U.S. Pat. No. 4,340,183to Kegel et al., granted Jul. 20, 1982. The irrigation system of Kegelet al. includes a main irrigation portion comprising a plurality ofirrigator spans connected in an end-to-end manner and extending radiallyfrom a center pivot tower. A corner irrigator span extends radially fromthe main irrigation portion. Movement of the corner irrigator span isbased on position data relayed to a microprocessor from a series of fourencoders. The first encoder is positioned between the main irrigationportion and the corner irrigator span. The first encoder relays acontrol signal to the microprocessor that represents an operating anglebetween the main irrigation portion and the corner irrigator span. Thesecond and third encoders are positioned on drive wheels of two adjacentirrigator spans in the main irrigation portion to determine a positionof these irrigator spans relative to a reference line. The second andthird encoders are responsive to the drive wheels to send a controlsignal to the microprocessor that represents the relative controlposition of the each of the respective spans to the reference line basedon the movement of the drive wheels. The fourth encoder is positionednear a steering unit of the corner irrigator span to determine anangular position of the steering unit. The fourth encoder sends acontrol signal to the microprocessor that represents the angularposition of the steering unit, i.e., the position of the drive wheels.Using the information relayed by the encoders, the microprocessor iscapable of controlling the steering unit of the corner irrigator spanduring operation to move the corner irrigator span along the outerboundary of the region.

[0008] Although the irrigation system of the '183 patent solves theproblem of using a buried conductor, other disadvantages of theirrigation system result. For instance, the second and third encodersmay be subject to error based on the inconsistent motion of the drivewheels of the irrigator spans to which they are attached. The drivewheels may slip or rut. With such irregular movement and inconsistenciesin the position of the main irrigation portion, difficulties arise whenthe irrigation system is used for fertilizer or pesticide application,or other applications that require higher precision. As a result, thereis a need in the art for an irrigation system that does not relystrictly on mechanical measurements to determine control positions forthe main irrigation portion.

SUMMARY OF THE INVENTION AND ADVANTAGES

[0009] The present invention provides an irrigation system for conveyinga fluid to a region having a main boundary and an outer boundaryoutlying the main boundary. The irrigation system includes a centerpivot. A main irrigation portion has a proximal end at the center pivot.The main irrigation portion extends radially to a distal end forrotation about the center pivot to irrigate the region within the mainboundary. A corner irrigator span is coupled to the main irrigationportion. The corner irrigator span extends radially from the distal endof the main irrigation portion to irrigate the region between the mainboundary and the outer boundary. A main drive system moves the mainirrigation portion about the center pivot and along the main boundary. Acorner drive system moves the corner irrigator span with the mainirrigation portion and along the outer boundary. A first electricalgenerator operates between the corner irrigator span and the mainirrigation portion to generate a first control signal representing anoperating angle between the corner irrigator span and the mainirrigation portion. A second electrical generator is coupled to the mainirrigation portion to generate a second control signal representing aprimary control position of the main irrigation portion. A controller isprogrammed to receive the control signals and control the corner drivesystem based on the control signals to maintain a target operating anglebetween the corner irrigator span and the main irrigation portion. Theirrigation system is characterized by the second electrical generatorbeing a position determining sensor for sensing a reference signal todetermine the primary control position.

[0010] A method of controlling the irrigation system is also provided.The method of controlling the irrigation system begins by moving themain irrigation portion and the corner irrigator span about the centerpivot in an operating mode. A plurality of current values for anoperating angle between the main irrigation portion and the cornerirrigator span are determined as the main irrigation portion and thecorner irrigator span move. At the same time, a reference signal issensed and a plurality of current values for a primary control positionbased on the sensed reference signal are determined. A steering unit iscontrolled based on the plurality of current values determined for theoperating angle and the primary control position.

[0011] The present invention provides several advantages over the priorart. One advantage is the ability of the irrigation system to preciselydetermine the primary control position of the main irrigation portionwithout relying strictly on mechanical measurements. Instead, theposition determining sensor senses a reference signal to determine theprimary control position. By utilizing such a device, the disadvantagesof mechanical measurements are alleviated. This results in bettercontrol of application rates such that the irrigation system can be usedto spray chemicals such as herbicides and pesticides to the region.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Other advantages of the present invention will be readilyappreciated as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings wherein:

[0013]FIG. 1 is a perspective view of an irrigation system embodying thepresent invention;

[0014]FIG. 2 is a perspective view of a main irrigation portion of theirrigation system;

[0015]FIG. 2A is a perspective view of an alternative embodiment of amain irrigation portion of an irrigation system;

[0016]FIG. 3 is a top view illustrating an end irrigator span and acorner irrigator span;

[0017]FIG. 4 is a perspective view of a sliding joint between the endirrigator span and the corner irrigator span;

[0018]FIG. 5 is a block diagram of a control system of the presentinvention; and

[0019]FIG. 6 is a schematic view of the irrigation system of the presentinvention illustrating positions of the corner irrigator span and themain irrigation portion about the region.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Referring to the Figures, wherein like numerals indicate like orcorresponding parts throughout the several views, an irrigation systemfor conveying a fluid from a fluid source 12 to a region A is generallyshown at 10. The irrigation system 10 of the present invention can beused for a multitude of purposes. Therefore, it is to be understood thatthe fluid could include many different substances. The fluid could bewater for irrigating crops in a field. The fluid could also be a mixtureof water and chemicals for controlling pests such as insects and fungior for controlling weeds such as grasses, thistle, ragweed, nightshade,cocklebur, and so on. The irrigation system 10 could also be used toapply fertilizers to the field. Likewise, the fluid source 12 may be atank containing chemicals or fertilizers, a water source, and so on.

[0021] Referring to FIG. 1, a center pivot tower 13 is positionedadjacent to the fluid source 12. A plurality of irrigator spans 14 arepivotally interconnected in an end-to-end manner from the center pivottower 13. The irrigator spans 14 extend radially from the center pivottower 13. These interconnected irrigator spans 14 constitute a mainirrigation portion 16 of the irrigation system. The irrigator spans 14rotate together in the main irrigation portion 16 about the center pivottower 13. A heavy-duty swivel 15 pivotally interconnects the irrigatorspan 14 adjacent to the center pivot tower 13 with the center pivottower 13 to allow rotation of the main irrigation portion 16 about thecenter pivot tower 13.

[0022] Referring to FIG. 2, joints 18 interconnect the irrigator spans14 of the main irrigation portion 16. The joints 18 may be a ball andsocket type connection or a tongue and pin connection. The joints 18 areflexible to allow relative radial movement between the irrigator spans14.

[0023] Individual drive systems 20 move each of the irrigator spans 14radially about the center pivot tower 13 to irrigate the region A withina main boundary M of the region A (see FIG. 6). Each drive system 20comprises a drive motor 22, a pair of gearboxes (not shown), two drivewheels 26, and a variable frequency drive module 28 to control the speedof the drive motor 22. A drive tower 30 supports each of the drivesystems 20. The gearboxes are positioned on opposite sides of the drivemotor 22 and are connected to the drive motor 22 by a pair of driveshafts. Each of the variable frequency drive modules 28 control themovement of the respective irrigator span 14 by varying the speed of therespective drive motor 22.

[0024] Each of the irrigator spans 14 further includes a supportstructure 34 and a conduit 36 supported by the support structure 34.Each of the conduits 36 is in fluid communication with each other andthe fluid source 12. The fluid from the fluid source 12 travels throughthe conduits 36 to a plurality of discharge nozzles 38 that are spacedalong the conduits 36 to spray the fluid onto the region A. A coupling40 provides a flexible connection between each of the conduits 36 toallow vertical and radial movement of the conduits 36 relative to oneanother. The present invention could be practiced with any number ofirrigator spans 14 extending radially from the center pivot tower 13 inthe main irrigation portion 16.

[0025] Alignment mechanisms (not shown) are used to maintain alignmentbetween the irrigator spans 14 within predetermined limits as theirrigation system 10 rotates about the center pivot tower 13. Thealignment mechanisms are further described in co-pending applicationSer. No. 09/970,564, filed Oct. 4, 2001, herein incorporated byreference.

[0026] Referring to FIGS. 1 and 3, a corner irrigator span 42 extendsradially from the last irrigator span 44 extending radially from thecenter pivot tower 13 in the main irrigation portion 16. Hence, thecorner irrigator span 42 extends radially from the main irrigationportion 16. The last irrigator span shall be hereinafter described as anend irrigator span 44.

[0027] Referring specifically to FIG. 3, the corner irrigator span 42has a proximal end 46 and a distal end 48. The corner irrigator span 42further includes a corner support structure 50 (shown in FIG. 1, but notFIG. 3 for clarity) and a corner conduit 52 supported by the cornersupport structure 50. A plurality of discharge nozzles 53 (shown in FIG.1, but not FIG. 3 for clarity) are spaced along the corner conduit 52 tospray the fluid from the corner conduit 52 onto the region A between themain boundary M and an outer boundary B (see FIG. 6). A corner coupling54 flexibly interconnects the conduit 36 from the end irrigator span 44and the corner conduit 52. Thus, the corner conduit 52 is in fluidcommunication with each of the conduits 36 of the main irrigationportion 16 and the fluid source 12.

[0028] Referring to FIG. 3, a sliding joint 56 connects the proximal end46 of the corner irrigator span 42 to the end irrigator span 44.Referring to FIG. 4, the sliding joint 56 includes a housing 58pivotally supported on a pivot 59 mounted to the end irrigator span 44.The housing 58 defines a slot 60 for receiving the proximal end 46 ofthe corner irrigator span 42. More specifically, a joint member 62 fixedto the proximal end 46 of the corner irrigator span 42 moves linearlywithin the slot 60 relative to the housing 58 and the end irrigator span44. This movement is indicated by the two-headed arrow. Rollers 64 arepositioned on opposite sides of the joint member 62. The rollers 64 rolllinearly along a base 66 of the housing 58. Hence, the corner irrigatorspan 42 moves linearly relative to the end irrigator span 44, as well asradially. The housing 58 includes a stop plate 68 to prevent the jointmember 62 from rolling entirely through the slot 60. A reinforcementmember (not shown) slidably couples the housing 58 and the cornerirrigator span 42 to provide additional rigidity to the sliding joint 56when the housing 58 pivots with the corner irrigator span 42 relative tothe end irrigator span 44 about the pivot 59.

[0029] Referring back to FIG. 3, a corner drive system 70 moves thecorner irrigator span 42 with the main irrigation portion 16 about thecenter pivot tower 13. The corner drive system 70 moves the cornerirrigator span 42 along the outer boundary B as the main irrigationportion 16 moves within the main boundary M. The corner drive system 70comprises a corner drive unit 72 and a steering unit 74.

[0030] The corner drive unit 72 comprises a pair of corner drive motors76, each coupled to a drive wheel 78, and a corner variable frequencydrive module 80 to control the speed of the corner drive motors 76. Thecorner drive motors 76 are mounted to a corner drive tower 82 thatsupports the corner drive system 70. The corner variable frequency drivemodule 80 controls the speed of the corner irrigator span 42 by varyingthe speed of the corner drive motors 76.

[0031] The steering unit 74 includes a steering motor 84 and a variablefrequency drive module 89 to control the steering motor 84. The steeringmotor 84 pivots the drive wheels 78 to steer the corner irrigator span42 along the outer boundary B. The steering motor 84 pivots the drivewheels 78 via steering linkage 88 and steering shafts 86, as is wellknown to those skilled in the art.

[0032] The corner irrigator span 42 is movable through a wide range ofpositions relative to the end irrigator span 44 to provide bettercoverage to the region A. In other words, given a typical rectangularregion A, the corner irrigator span 42 provides flexibility in theirrigation system to better reach the outer boundary B of the region A.The corner irrigator span 42 is intended to be oriented at an operatingangle α relative to the end irrigator span 44. See FIG. 3. Conversely,the irrigator spans 14 of the main irrigation portion 16 are intended tomaintain radial alignment from the center pivot tower 13. See FIG. 1.

[0033] Referring to FIG. 5, a control system 90 controls movement of thecorner irrigator span 42. The control system 90 comprises two separatesystems to control the movement of the corner irrigator span 42. Thefirst system is a linear movement control system 92. The linear movementcontrol system 92 controls the corner drive unit 72 of the cornerirrigator span 42 as the corner irrigator span 42 moves across theregion A. The second system is a steering control system 94. Thesteering control system 94 controls the steering unit 74 to steer thecorner irrigator span 42 as the corner irrigator span 42 moves along theouter boundary B.

[0034] Referring to FIGS. 3, 4 and 5, the linear movement control system92 includes an electrical generator 96 that is operative between thehousing 58 and the joint member 62 to sense the linear movement of thejoint member 62 within the housing 58. The electrical generator 96 ispreferably a rotary potentiometer 96 capable of generating a variablesignal dependent upon the relative linear movement. The potentiometer 96provides a control signal that varies as the linear movement of thejoint member 62 within the housing 58 varies. The potentiometer 96transmits the control signal to the corner variable frequency drivemodule 80 such that as the control signal varies, the speed of thecorner drive motors 76 vary proportionally. This ensures that the cornerirrigator span 42 maintains pace with the main irrigation portion 16 asboth move about the center pivot tower 13 to irrigate the region A.Referring specifically to FIG. 4, an actuator 98 actuates thepotentiometer 96. The actuator 98 has a first end fixed to an actuationshaft (not shown) of the potentiometer 96 to actuate the potentiometer96. As is well known to those skilled in the art, as the actuation shaftrotates, the control signal varies. The actuator 98 has a second endslidably and rotatably coupled to the joint member 62 at the proximalend 46 of the corner irrigator span 42.

[0035] Referring to FIG. 5, the steering control system 94 includes acontroller 100 having a microprocessor (not shown) and memory (notshown) for controlling the steering unit 74. The steering control system94 utilizes control signals from four electrical generators102,104,106,108 to control the steering unit 74. Each of the electricalgenerators 102,104,106,108 will be described in turn.

[0036] Referring to FIG. 3, a first electrical generator 102 isoperative between the end irrigator span 44 and the corner irrigatorspan 42 to measure the operating angle α between the corner irrigatorspan 42 and the end irrigator span 44. The first electrical generator102 provides a first control signal to the controller 100 that varies asthe operating angle α between the end irrigator span 44 and the cornerirrigator span 42 varies. The first electrical generator 102 may be apotentiometer, a brushless angle resolver, or other device capable ofgenerating a variable signal dependent upon the relative angularmovement of the end irrigator span 44 to the corner irrigator span 42.The first electrical generator 102 is mounted to the end irrigator span44. A second actuator 110 actuates the first electrical generator 102 togenerate the first control signal. A first end of the second actuator110 is pivotally supported by the housing 58. See FIG. 4. A second endof the second actuator 110 is pivotally coupled to a sensing arm 111 ofthe first electrical generator 102. The sensing arm 111 is coupled to anactuation shaft (not shown) of the first electrical generator 102 torotate the actuation shaft and actuate the first electrical generator102. As is well known to those skilled in the art, as the actuationshaft rotates, the first control signal varies. In this configuration,as the housing 58 pivots about the pivot 59 with the corner irrigatorspan 42 and relative to the end irrigator span 44, the second actuator110 moves the sensing arm 111 to vary the first control signal that issent to the controller 100.

[0037] A second electrical generator 104 is coupled to the mainirrigation portion 16 to generate a second control signal representing aprimary control position P of the main irrigation portion 16. The secondelectrical generator 104 is a position determining sensor 104 fixed tothe end irrigator span 44. Preferably, the position determining sensor104 is a digital, three-axis electronic compass 104 capable ofgenerating the second control signal representing the primary controlposition P of the main irrigation portion 16. The electronic compass 104uses magnetic sensors (not shown) with MR technology to sense areference signal, e.g., the horizontal and vertical components of theearth's magnetic field, to provide position information. The electroniccompass 104 is electronically gimbaled using a two-axis (pitch and roll)tilt sensor (not shown) to give accurate heading readings even when theelectronic compass 104 is tilted up to forty degrees. The electroniccompass 104 is reliable and rugged and does not contain any movingcomponents. The electronic compass 104 sends the corresponding secondcontrol signal to the controller 100. Since the electronic compass 104is fixed relative to the end irrigator span 44, as the end irrigatorspan 44 rotates about the center pivot tower 13, the heading changes andthe second control signal varies accordingly.

[0038] A third electrical generator 106 is coupled to the mainirrigation portion 16 to generate a third control signal representing asecondary control position S of the main irrigation portion 16. Like thesecond control signal, the third control signal, and hence, thesecondary control position S, vary as the main irrigation portion 16rotates about the center pivot tower 13. Preferably, the thirdelectrical generator 106 is an angle resolver 106 that measures an angleof rotation of the irrigator span 14 adjacent to the center pivot tower13 about the center pivot tower 13. See FIGS. 1 and 2. The angleresolver 106 is fixed to an arm 105 extending from the irrigator span 14adjacent to the center pivot tower 13. The angle resolver 106 iscentered over a shaft 107 that defines an axis of rotation of the mainirrigation portion 16 about the center pivot tower 13. An actuationshaft (not shown) of the angle resolver 106 is coupled to the shaft 107and both are fixed from movement relative to the main irrigation portion16. Hence, as the angle resolver 106 rotates with the main irrigationportion 16 and relative to the shaft 107, the angle resolver 106 isactuated. As is well known to those skilled in the art, as the actuationshaft rotates, the third control signal varies. The third electricalgenerator 106 may be a potentiometer, a brushless angle resolver, orother device capable of generating a variable control signal dependentupon the position of one of the irrigator spans 14. In the alternativeembodiment, illustrated in FIG. 2A, the third electrical generator 106is an electronic compass 106 fixed to the irrigator span 14 adjacent tothe center pivot tower 13 and identical to the electronic compass 104 onthe end irrigator span 44.

[0039] Referring back to FIG. 3, a fourth electrical generator 108 isresponsive to pivoting, e.g., steering, of the drive wheels 78 by thesteering unit 74 such that the fourth electrical generator 108 iscapable of generating a fourth control signal that varies as the drivewheels 78 of the corner irrigator span 42 are steered in the region A.Hence, the fourth control signal represents a steering angle Ψ of thedrive wheels 78 relative to a reference line parallel to a center axisof the corner irrigator span 42. The fourth control signal is alsotransmitted to the controller 100. The fourth electrical generator 108may be a potentiometer, a brushless angle resolver, or other devicecapable of generating a variable signal dependent upon the steeringangle Ψ of the drive wheels 78 of the corner irrigator span 42. A thirdactuator 112, similar to the second actuator 110, actuates the fourthelectrical generator 108. The third actuator 112 includes a first endpivotally coupled to the steering linkage 88 and a second end coupled toan actuation shaft (not shown) of the fourth electrical generator 108 torotate the actuation shaft and actuate the fourth electrical generator108. As is well known to those skilled in the art, as the actuationshaft rotates, the fourth control signal varies.

[0040] After the controller 100 receives the control signals from theelectrical generators 102,104,106,108, the controller 100 processesthese control signals to ultimately control the steering unit 74. Priorto operating the irrigation system 10 in an operating mode, however, thesteering control system 94 must learn the outer boundary B of the regionA. In other words, before the steering control system 94 can control thesteering unit 74, the steering control system 94 must understand wherethe corner irrigator span 42 is to be positioned in the region A duringoperation.

[0041] Referring to FIG. 6, the region A is bounded by the outerboundary B. The goal of the steering control system 94 is to ensure thatthe corner irrigator span 42 follows the outer boundary B. It is to beappreciated that FIG. 6 illustrates four irrigator spans 14 in the mainirrigation portion 16. A series of primary P1-P7 and secondary S1-S7control positions of the main irrigation portion 16 are shown toillustrate the change in these positions P,S as the irrigation systemrotates about the center pivot tower 13 during operation. A series ofoperating angles α1-α7 illustrate the change in the operating angle α asthe corner irrigator span 42 rotates relative to the end irrigator span44 to reach the outer boundary B during operation. A series of steeringangles Ψ1-Ψ7 illustrate the change in the steering angle Ψ of the drivewheels 78 of the corner irrigator span 42 as the corner irrigator span42 rotates relative to the end irrigator span 44 to reach the outerboundary B during operation.

[0042] Prior to operating the irrigation system, these positions P1-P7and S1-S7 and angles α1-α7 and Ψ1-Ψ7 are programmed into the controller100. In other words, for each primary P and secondary S controlposition, there is a corresponding operating angle α, and steering angleΨ. This teaching is performed in a teaching mode of the controller 100.It should be appreciated that the number of positions and anglesdescribed herein is for illustrative purposes only. Furthermore, FIG. 6only illustrates one quarter of a typical region A. The controller 100would actually need to learn the positions and angles for the entireregion A, i.e., for 360 degrees about the center pivot tower 13. In theteaching mode, an operator manually controls the corner drive system 70using an input device to steer the drive wheels 78 of the cornerirrigator span 42 along the outer boundary B, while the controller 100receives the control signals corresponding to the positions and anglesto be programmed therein.

[0043] The positions and angles from the teaching mode are stored in alook-up table in the controller 100. The controller 100 refers to thelook-up table during operation of the irrigation system 10 to controlthe steering unit 74. For example, with reference to FIG. 6, the look-uptable may look similar to Table 1 below. TABLE 1 Primary ControlSecondary Position Control Position Operating Angle Steering Angle P1-P7S1-S7 α1-α7 Ψ1-Ψ7 276° 277°  95° 10° 286° 287° 125° 35° 296° 297° 145°55° 306° 307° 175°0 80° 316° 317° 155°0 60° 326° 327° 145°0 40° 336°337° 120°0 15°

[0044] In the preferred embodiment, the control signals from theelectrical generators 102,104,106,108 are relayed to the controller 100every tenth of a degree while in the teaching mode. Therefore, since theirrigation system 10 revolves three hundred sixty degrees about thecenter pivot tower 13, thirty-six hundred positions and angles arerecorded.

[0045] Once the controller 100 has generated the look-up table in theteaching mode, the controller 100 is ready to automatically control thesteering unit 74 as the irrigation system moves across the region A inthe operating mode using the data in the look-up table.

[0046] Operation of the irrigation system 10 in the operating mode willnow be described. A pacing speed of the drive motor 22 of the endirrigator span 44 is adjusted at a main control panel (not shown) to auser-defined rate. Accordingly, the drive system 20 of the end irrigatorspan 44 paces the irrigation system 10. In a first series of steps, thecontroller 100 receives the control signals from the electronic compass104 and the third electrical generator 106. The controller 100 thendetermines current values of the primary P and secondary S controlpositions. These current values are then averaged. The average value isthen compared to an average of the initial values in the look-up table.The average values are used to compensate for curl of the mainirrigation portion 16, as illustrated by hidden lines in FIG. 6. Asshown, curling of the main irrigation portion 16 can have a dramaticeffect on positioning of the corner irrigator span 42. This effect isreduced by averaging the primary P and secondary S control positions.

[0047] In a second series of steps, using the first row of Table 1 forillustration, a target operating angle α1 and target steering positionΨ1 corresponding to the average of the current values of the controlpositions P,S is retrieved from the look-up table. The controller 100compares the average of the current values of the control positions P,Sto the average of the initial values of the control positionsP1-P7,S1-S7 in the look-up table and retrieves the target operatingangle α1 and target steering angle Ψ1 corresponding to the closestaverage of the initial values of the control positions P1,S1.

[0048] With the target operating angle α1 and target steering angle Ψ1from the look-up table, the controller 100 performs a third series ofsteps. In the third series of steps, the controller 100 controls thesteering unit 74 to ensure that the corner irrigator span 42 follows theouter boundary B. In the third series of steps, the controller 100 firstreceives the first control signal from the first electrical generator102 and converts the control signal into a current value of theoperating angle α. The controller 100 then determines if the currentvalue of the operating angle α is equal to the target operating angleα1. If so, then no adjustment needs to be made, i.e., the cornerirrigator span 42 is at the target operating angle.

[0049] If the current value of the operating angle α is not equal to thetarget operating angle α1, then adjustment of the drive wheels 78 viathe steering unit 74 must be made to bring the corner irrigator span 42into correct position. To start, the controller 100 determines whetherthe current value of the operating angle α is greater than or less thanthe target operating angle α1. In either case, the next step is for thecontroller 100 to determine a deviation from the target operating angleα1 based on the difference between the current value of the operatingangle α and the target operating angle α1. Next, the controller 100instructs, i.e., sends an output signal to, the steering unit 74 to turnthe drive wheels 78 either clockwise or counterclockwise, depending onwhether the current value of the operating angle α is greater than orless than the target operating angle α1. The amount that the drivewheels 78 are turned depends on the deviation. A scaled parameter, basedon the deviation, is used to vary the amount that the drive wheels 78are turned. The steering unit 74 then turns the drive wheels 78 tochange a current value of the steering angle Ψ accordingly until thecurrent value of the operating angle α is equal to the target operatingangle α1, then the steering unit 74 returns the drive wheels 78 to thetarget steering angle Ψ1. The first, second, and third series of stepsare continuously repeated to ensure that the corner irrigator span 42follows along the outer boundary B.

[0050] The input and output signals used to control the corner driveunit 72 and the steering unit 74 are illustrated by signal lines witharrowheads in FIG. 3 and FIG. 5.

[0051] In the preferred embodiment, the irrigator spans, the supportstructures, the drive towers, and the conduits are made from galvanizedsteel. Any suitable material may be used, such as, but not limited topainted steel, iron, aluminum, and so on. The couplings are made from arubber polymer, but may be made from any number of materials creating aflexible connection such as, but not limited to, thermoplastic polymers,flexible plastics, and so on. The motors are reversible, variable speed,AC motors. The connections between the electrical generators and powersources and electrical service such as that between the motors andvariable frequency drive modules are not shown in the FIGS. for clarity,but are well understood by those skilled in the art.

[0052] Obviously, many modifications and variations of the presentinvention are possible in light of the above teachings. The inventionmay be practiced otherwise than as specifically described within thescope of the appended claims, wherein that which is prior art isantecedent to the novelty set forth in the “characterized by” clause.The novelty is meant to be particularly and distinctly recited in the“characterized by” clause whereas the antecedent recitations merely setforth the old and well-known combination in which the invention resides.These antecedent recitations should be interpreted to cover anycombination in which the incentive novelty exercises its utility. Inaddition, the reference numerals in the claims are merely forconvenience and are not to be read in any way as limiting.

What is claimed is:
 1. An irrigation system (10) for conveying a fluidto a region (A) having a main boundary (M) and an outer boundary (B)outlying the main boundary (M), said system comprising; a center pivot(13), a main irrigation portion (16) having a proximal end at saidcenter pivot (13) and radially extending to a distal end for rotationabout said center pivot (13) to irrigate the region (A) within the mainboundary (M), a corner irrigator span (42) coupled to said mainirrigation portion (16) and radially extending from said distal end ofsaid main irrigation portion (16) for irrigating the region (A) betweenthe main boundary (M) and the outer boundary (B), a drive system formoving said main irrigation portion (16) about said center pivot (13)and along the main boundary (M), a corner drive system (70) for movingsaid corner irrigator span (42) with said main irrigation portion (16)and along the outer boundary (B), a first electrical generator (102)operative between said corner irrigator span (42) and said mainirrigation portion (16) for generating a first control signalrepresenting an operating angle (α) between said corner irrigator span(42) and said main irrigation portion (16) whereby the first controlsignal varies as the operating angle (α) varies, a second electricalgenerator (104) coupled to said main irrigation portion (16) forgenerating a second control signal representing a primary controlposition (P) of said main irrigation portion (16) whereby the secondcontrol signal varies as the primary control position (P) varies, and acontroller (100) programmed for receiving said control signals andcontrolling said corner drive system (70) based on said control signalsto maintain a target operating angle between said corner irrigator span(42) and said main irrigation portion (16) to ensure that said cornerirrigator span (42) follows along the outer boundary (B), said systemcharacterized by said second electrical generator (104) being a positiondetermining sensor (104) for sensing a reference signal to determine theprimary control position (P) of said main irrigation portion (16).
 2. Anirrigation system (10) as set forth in claim 1 wherein said positiondetermining sensor (104) is further defined as an electronic compass(104).
 3. An irrigation system (10) as set forth in claim 2 wherein saidmain irrigation portion (16) comprises a plurality of irrigator spans(14) interconnected in an end-to-end manner and said electronic compass(104) is fixed to one of said irrigator spans (14).
 4. An irrigationsystem (10) as set forth in claim 3 wherein said plurality of irrigatorspans (14) include an end irrigator span (44) at said distal end of saidmain irrigation portion (16) and said first electrical generator (102)operates between said end irrigator span (44) and said corner irrigatorspan (42) to generate the first control signal.
 5. An irrigation system(10) as set forth in claim 4 wherein said electronic compass (104) isfixed to said end irrigator span (44).
 6. An irrigation system (10) asset forth in claim 5 further including a third electrical generator(106) coupled to said main irrigation portion (16) for generating athird control signal representing a secondary control position (S) ofsaid main irrigation portion (16) whereby the third control signalvaries as the secondary control position (S) varies.
 7. An irrigationsystem (10) as set forth in claim 6 wherein said corner drive system(70) includes a steering unit (74) and a corner drive unit (72).
 8. Anirrigation system (10) as set forth in claim 7 further including afourth electrical generator (108) responsive to said steering unit (74)for generating a fourth control signal representing a steering angle (Ψ)of said steering unit (74).
 9. An irrigation system (10) as set forth inclaim 8 wherein said controller (100) is programmed for receiving thecontrol signals and controlling said steering unit (74) based on thecontrol signals to maintain movement of said corner irrigator span (42)along the outer boundary (B).
 10. An irrigation system (10) as set forthin claim 9 wherein said drive system is further defined as a pluralityof drive systems (20) for moving each of said plurality of irrigatorspans (14) of said main irrigation portion (16) about said center pivot(13).
 11. An irrigation system (10) as set forth in claim 10 furtherincluding an electrical generator (96) operative between said endirrigator span (44) and said corner irrigator span (42) for generating acontrol signal representing linear movement of said corner irrigatorspan (42) relative to said end irrigator span (44) whereby the controlsignal varies as a linear distance between said corner irrigator span(42) and said end irrigator span (44) varies.
 12. An irrigation system(10) as set forth in claim 11 wherein said electrical generator (96)operative between said end irrigator span (44) and said corner irrigatorspan (42) is further defined as a potentiometer (96).
 13. An irrigationsystem (10) as set forth in claim 12 wherein said corner drive unit (72)comprises a corner variable frequency drive module (80) and at least onecorner drive motor (76) having variable speed and said corner variablefrequency drive module (80) receives the control signal from saidpotentiometer (96) to vary the speed of said at least one corner drivemotor (76).
 14. An irrigation system (10) as set forth in claim 8wherein said first (102), third (106), and fourth (108) electricalgenerators are further defined as angle resolvers.
 15. An irrigationsystem (10) as set forth in claim 8 wherein said first (102) and fourth(108) electrical generators are further defined as angle resolvers andsaid third electrical generator (106) is further defined as anelectronic compass (106).
 16. A method of controlling an irrigationsystem (10) comprising a main irrigation portion (16) coupled to acenter pivot (13) and a corner irrigator span (42) extending radiallyfrom the main irrigation portion (16), said method comprising the stepsof; moving the main irrigation portion (16) and the corner irrigatorspan (42) about the center pivot (13) in an operating mode, determininga plurality of current values for an operating angle (a) between themain irrigation portion (16) and the corner irrigator span (42) as themain irrigation portion (16) and the corner irrigator span (42) moveabout the center pivot (13) in the operating mode, sensing a referencesignal as the main irrigation portion (16) and the corner irrigator span(42) move about the center pivot (13) in the operating mode, determininga plurality of current values for a primary control position (P) fromthe sensed reference signal as the main irrigation portion (16) and thecorner irrigator span (42) move about the center pivot (13) in theoperating mode, and automatically controlling the steering unit (74)based on the plurality of current values for the operating angle (a) andthe primary control position (P).
 17. A method as set forth in claim 16further including determining a plurality of current values for asecondary control position (S) from the sensed reference signal as themain irrigation portion (16) and the corner irrigator span (42) moveabout the center pivot (13) in the operating mode and automaticallycontrolling the steering unit (74) based on the plurality of currentvalues for the operating angle (α) and the primary (P) and secondary (S)control positions.
 18. A method as set forth in claim 17 furtherincluding moving the main irrigation portion (16) and the cornerirrigator span (42) about the center pivot (13) in a teaching mode priorto the operating mode and compiling a plurality of initial values forthe operating angle (α) and the primary (P) and secondary (S) controlpositions in a look-up table in the teaching mode.
 19. A method as setforth in claim 18 further including steering the corner irrigator span(42) about the center pivot (13) as the corner irrigator span (42) movesabout the center pivot (13) in the teaching mode and compiling aplurality of initial values of a steering angle (Ψ) of the steering unit(74) of the corner irrigator span (42) in the look-up table while thesteering unit (74) steers the corner irrigator span (42) about thecenter pivot (13) in the teaching mode.
 20. A method as set forth inclaim 19 further including comparing the plurality of current valuesdetermined in the operating mode with the plurality of initial valuescompiled in the teaching mode and determining a target operating anglefrom the look-up table based on the comparison.
 21. A method as setforth in claim 20 further including automatically steering the steeringunit (74) in a direction toward achieving the target operating angle.22. A method as set forth in claim 21 further including determining atarget steering angle from the look-up table that corresponds to thedetermined target operating angle and steering the steering unit (74) tothe target steering angle upon achieving the target operating angle.